Electromechanical actuator comprising a mechanical roller torque limiter

ABSTRACT

An electromechanical actuator comprising a body and an electric motor driving at least one motion transmission element connected to the body via a brake device, a mechanical torque limiter with rollers, and a unidirectional transmission member, the brake device including an electrical activator member so that when the activator member is powered, the unidirectional transmission member is released relative to the body, and when the activator member is not powered, the unidirectional transmission member is secured to the body and opposes pivoting of the transmission element in one direction of rotation up to a maximum transmissible torque defined by the torque limiter.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to moving a movable element relative to afixed body, and more precisely it relates to an electromechanicalactuator suitable for use by way of example in aviation, and inparticular for moving a flight control surface relative to the structureof an aircraft. By way of example, such a flight control surface may bean aileron, an elevon, a flap, a rudder control surface, an elevator, aspoiler, . . . .

Aircraft generally comprise a fixed structure, such as a wing or a tail,having flight control surfaces hinged thereto that are mounted on thefixed structure so as to pivot. Actuators connect the movable surfacesmechanically to the fixed structure and are themselves connected so asto be controlled by a control unit on which the pilot of the aircraftacts.

Description of Related Art

Actuators are known that comprise an electric motor and a motiontransmission element driven by a rotor of the electric motor. Generally,in such actuators, the electric motor has a stator secured to a bodythat is fastened to the fixed structure, and a transmission elementdrives an inlet element of a transmission system such as a screw-and-nutassembly and/or stepdown gearing, with an outlet element fastened to theflight control surface so that a movement of the outlet element causesthe flight control surface to pivot between a deployed position and aretracted position or a neutral position.

In the event of a failure of the motor or of its control means, anddepending on the type of flight control surface, it may be preferable toleave the flight control surface free to move towards one of itspositions while preventing the flight control surface from movingtowards the second of its positions, e.g. under the effect ofaerodynamic forces. For this purpose, the transmission assemblygenerally includes an overrunning clutch or “freewheel” that can becomeclutched in the event of motor failure in order to oppose pivoting ofthe transmission element in the direction corresponding to the flightcontrol surface moving towards its second position.

When the freewheel is clutched, the flight control surface tending tomove towards its deployed position exerts a torque on the transmissionelement, which torque is transmitted to the body. Under certaincircumstances, the torque can be large and risks damaging the entiretransmission system all the way to the structure of the aircraft.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to remedy that drawback.

To this end, the invention provides an electromechanical actuatorcomprising a body, an electric motor having a stator fastened to thebody, and at least one motion transmission element rotatably connectedto a rotor of the motor, said element being connected to the fixed bodyvia a unidirectional transmission member and a brake device. Theactuator includes a mechanical torque limiter with rollers and the brakedevice includes an electrical activator member so that when theactivator member is powered, the unidirectional transmission member isreleased relative to the body, and when the activator member is notpowered, the unidirectional transmission member is secured to the bodyand opposes pivoting of the transmission element in one direction ofrotation up to a maximum transmissible torque defined by the mechanicaltorque limiter with rollers.

Thus, in the event of excessive torque, the torque limiter allows thetransmission element to slide relative to the body, thereby limiting anyrisk of damaging the body.

Advantageously, the mechanical torque limiter with rollers is mountedbetween the body and the unidirectional transmission member.

This embodiment has a structure that is particularly compact and makesit possible to incorporate the brake device, the unidirectionaltransmission member, and the mechanical torque limiter with rollers in asingle subassembly.

Preferably, the mechanical torque limiter with rollers is mountedbetween the brake device and the unidirectional transmission member.

This arrangement makes it simple to incorporate the mechanical torquelimiter with rollers.

Other characteristics and advantages of the invention appear on readingthe following description of a particular, non-limiting embodiment ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the accompanying drawings, in which the sole FIGUREis a diagrammatic longitudinal section view of an actuator of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The actuator of the invention is described herein in an application tomoving a flight control surface relative to the structure of anaircraft. The flight control surface is movable between a deployedposition and a neutral or retracted position.

With reference to the sole FIGURE, the electromechanical actuatorcomprises a body 1 and an electric motor 2 having a stator fastened tothe body 1 and a rotor rotatably connected to a motion transmissionelement.

The body 1 has conventional means for fastening it to the structure ofan aircraft.

The electric motor 2 is powered by a control unit (not shown) that isconnected to the electricity network of the aircraft for its own powersupply and for powering the actuator, and that is connected to thecockpit of the aircraft to receive orders therefrom for deploying orretracting the flight control surface.

In this example, the motion transmission element is a shaft 3 pivotallymounted in the body 1 and connected to the flight control surface via amotion transmission assembly (not shown). By way of example, the motiontransmission assembly comprises a stepdown device and/or a motiontransformation device such as a screw-and-nut assembly, and has an inletelement rotatably connected to the shaft 3 and an outlet element e.g.connected to the free end of a lever that is connected to the flightcontrol surface. The shaft 3 is guided in rotation relative to the body1 by bearings (not shown) and it is connected to the body 1 via aunidirectional transmission member, specifically in this example afreewheel given overall reference 4, a torque limiter given overallreference 5, and a brake device given overall reference 6.

The freewheel 4 comprises an inner portion 4.1 secured to the shaft 3,an outer portion 4.2 pivotally mounted on the inner portion 4.1, and aratchet assembly allowing the outer portion 4.2 to turn in only onedirection of rotation.

The torque limiter 5 is a mechanical torque limiter with rollersincluding an inner sleeve 5.1 and an outer sleeve 5.2. The inner sleeve5.1 is fastened to the outer portion 4.2 of the freewheel 4 and theouter sleeve 5.2 is connected to rotate with an inner ring 6.1 of thebrake device 6.

In this example, the inner sleeve 5.1 is in the form of a tube centeredon the axis of rotation A of the shaft 3.

The outer sleeve 5.2 is also in the form of a tube centered on the axisA: the outer sleeve 5.2 surrounds the inner sleeve 5.1 and is pivotallyreceived in a bearing secured to the body 1. The outside surface of theouter sleeve 5.2 is fluted to receive the inner ring 6.1 in axialsliding.

The torque limiter 5 further comprises rollers 5.3 interposed betweenthe inner sleeve 5.1 and the outer sleeve 5.2, each roller 5.3 beingsuitable for moving along an inside surface of the outer sleeve 5.2 andfor being received in one of the housings 5.4 formed along thecircumference of said inside surface.

The torque limiter 5 further comprises springs 5.5, each spring 5.5being associated with one of the rollers 5.3 in such a manner as toexert a constant force on said roller 5.3 in order to press the roller5.3 against the inside surface of the outer sleeve 5.2.

In this example, the springs 5.5 are arranged in such a manner as toextend radially (i.e. perpendicularly to the axis of rotation A of theshaft 3) between the inner sleeve 5.1 and the outer sleeve 5.2, a firstend of each spring 5.5 being secured to the inner sleeve 5.1 and asecond end being connected to one of the rollers 5.3 in order to come topress said roller 5.3 against the inside surface of the outer sleeve5.2.

The radial force exerted by the springs 5.5 on the rollers 5.3 defines amaximum transmissible torque, i.e. the maximum torque that can betransmitted from the inner sleeve 5.1 to the outer sleeve 5.2: so longas this maximum transmissible torque is not exceeded, the springs 5.5hold the rollers 5.3 in place in the housings 5.4 and the sleeves 5.1and 5.2 remain secured to each other; as soon as the maximumtransmissible torque is exceeded, the springs 5.5 are compressed in sucha manner as to allow the rollers 5.3 to exit the housings 5.4 and toallow a relative movement of the two sleeves between each other by meansof the movement of the rollers 5.3 on the inside surface of the outersleeve 5.2.

In addition to the movable ring 6.1, the brake device 6 has an outerring 6.2 that is rigidly fastened to the body 1 (more precisely, theouter ring 6.2 in this example is a portion of the body 1) and an outerring 6.3 fastened to the body 1 with axial clearance. The inner ring 6.1is fastened with axial clearance to the outer sleeve 5.2 (the inner ring6.1 is more precisely engaged in the outside surface of the outer sleeve5.2) and has a portion with faces that are each provided with a frictionlining and that extend between friction linings carried by the outerrings 6.2 and 6.3. Springs 6.4 extend between the body 1 and the outerring 6.3 to clamp the inner ring 6.1 between the outer rings 6.3 and6.2. The brake device 6 also has an electrical activator member 6.5 inthe form of a solenoid dimensioned so that when it is powered itattracts the outer ring 6.3 and moves it away from the inner ring 6.1against the force exerted by the springs 6.4.

In operation, when the activator member 6.5 is powered, the shaft 3 canpivot in both directions of rotation (it should be observed that in thedirection passed by the freewheel 4, the motor 2 delivers little or nodrive to the inner ring 6.1 and the torque limiter 5) and, when theactivator member 6.5 is not powered, the freewheel 4 opposes rotation ofthe shaft 3 in one of the two directions of rotation. Thus, when theactivator member 6.5 is powered, the electric motor 2, which is alsopowered, drives the shaft 3 to turn in either of its directions ofrotation.

When the activator member 6.5 is not powered, the electric motor 2 islikewise not powered so that only aerodynamic forces acting on theflight control surface can cause the shaft 3 to pivot. Because of thefreewheel 4 opposing turning of the shaft 3 in one of the two directionsof rotation, the shaft 3 prevents the flight control surface from movingaway from its neutral position towards its deployed position, whereasthe flight control surface is left free to move towards its neutralposition. Nevertheless, if the aerodynamic forces acting on the flightcontrol surface exert a torque on the shaft 3 that is greater than themaximum torque that can be transmitted between the sleeves 5.1 and 5.2of the torque limiter 5, the inner sleeve 5.1 will pivot relative to theouter sleeve 5.2, thus allowing the shaft 3 to turn and allowing theflight control surface to move towards its deployed position. As aresult, the torque limiter 5 limits the torque that can be transmittedto the structure of the aircraft and to the body 1 via the shaft 3, thefreewheel 4, and the brake device 6 when the activator member is notpowered.

Naturally, the invention is not limited to the embodiments described butencompasses any variant coming within the ambit of the invention asdefined by the claims.

In particular, the mechanical torque limiter with rollers may be mounteddownstream from the one-way transmission member or between the brakedevice and the body.

The mechanical torque limiter with rollers could be in an arrangementthat differs from that described. In particular, although in thisexample the springs extend radially between the inner sleeve and theouter sleeve, the torque limiter could be shaped in such a manner thatthe springs extend axially between the two sleeves (i.e. they extendalong the axis A).

The one-way transmission member may make use of pawls, rollers, or ofchocking elements.

The invention claimed is:
 1. An electromechanical actuator comprising abody, an electric motor having a stator fastened to the body, and atleast one motion transmission element rotatably connected to a rotor ofthe motor, said element being connected to the body via a unidirectionaltransmission member and a brake device, the actuator being characterizedin that the actuator includes a mechanical torque limiter with rollersand in that the brake device comprises an electrical activator member sothat when the electrical activator member is powered, the unidirectionaltransmission member is released relative to the body, and when theelectrical activator member is not powered, the unidirectionaltransmission member is secured to the body and opposes pivoting of thetransmission element in one direction of rotation up to a maximumtransmissible torque defined by the mechanical torque limiter withrollers.
 2. The actuator according to claim 1, wherein the mechanicaltorque limiter with rollers is mounted between the body and theunidirectional transmission member.
 3. The actuator according to claim2, wherein the mechanical torque limiter with rollers is mounted betweenthe brake device and the unidirectional transmission member.
 4. Theactuator according to claim 3, wherein the mechanical torque limiterwith rollers comprises an inner sleeve connected to rotate with a firstportion of the unidirectional transmission member, an outer sleeveconnected to rotate with a first portion of the brake device, androllers interposed between the inner sleeve and the outer sleeve, thetorque limiter further including springs exerting a constant force onthe various rollers in order to temporarily secure the inner sleeve andthe outer sleeve as long as the maximum transmissible torque has notbeen exceeded.
 5. The actuator according to claim 4, wherein the springsare arranged in such a manner as to extend radially between the innersleeve and the outer sleeve, a first end of each spring being secured tothe inner sleeve and a second end of each spring coming to press aroller against an inside surface of the outer sleeve.
 6. The actuatoraccording to claim 1, wherein the unidirectional transmission member isa freewheel.